REPORT ON THE MAGNETICAL RESULTS. 7 



readily understood that it required considerable reinforcement from other sources before 

 they could be efficiently constructed, especially as they are dependent upon observation 

 alone. For this purpose every available observation chiefly obtained between the 

 years 1865-87 has been utilised, a large number being furnished by our vessels of war, 

 as well as many others from foreign publications. It is presumed that magneticians 

 are already sufficiently acquainted with the published sources of information on this 

 subject as not to require any special mention of them, but there are others the enumera- 

 tion of which may tend to add value to the charts. Thus, in the years 1874-76, a series 

 of observations of the inclination and force were made on the east coast of Africa by the 

 officers of H.M.S. "Nassau" with a Fox circle, and in 1885-86 a valuable series, com- 

 prising all three elements, was obtained with absolute instruments at certain stations 

 on the west coast of Australia, from Cape Leeuwin to Cossack inclusive, by H.M. 

 surveying vessel " Meda." 



That wild waste of waters, too, traversed by ships making their voyages from 

 Australia and New Zealand to Magellan Strait or Cape Horn, has not been neglected. 

 Observations of the declination made in H.M.S. "Esk" in 1867, and "Pearl," 1871 — 

 both being wooden ships— and lately, in 1885-86, in the New Zealand Steam Shipping 

 Company's iron ships, have added considerably to our knowledge of its distribution in 

 those seas. The results from the iron ships have been confirmed by those from 

 H.M.S. " Thalia," in 1887, a wooden vessel with but small errors affecting the compass. 



To combine this twenty years' observations usefully, a somewhat extended know- 

 ledge of the distribution and amount of secular change became a necessity. For certain 

 portions of the earth largely frequented this element of terrestrial magnetism has been 

 approximately determined — at fixed observatories with considerable precision ; and, 

 generally speaking, it is only there that its exact and variable value can be obtained, 

 for, as already shown, a distance of a few feet between two observers is quite enough to 

 considerably affect their results. 



Amongst other contributions to our knowledge of the secular change may be 

 mentioned those by Mr. C. A. Schott for the United States and Canada, and a few 

 other stations in Europe. This valuable series, which is the outcome of considerable 

 research, is treated both mathematically and graphically, and may be considered as 

 authoritative for North America as regards the secular change of the declination. 



The work carried out during the Voyage of the Challenger was of too world-wide 

 a character for any extended magnetic survey of the countries visited, such as that of 

 the United States, one great object being to visit certain positions in unfrequented and 

 widely different parts of the earth where previous observers had been, rather than the 

 beaten tracks. During the outward part of the voyage in 1873, St. Paul's Rocks, in the 

 Atlantic, were visited, and Ross's position when he landed in 1840 occupied as nearly as 

 possible. The position being apparently free from local magnetic disturbance, the 



